There is much interest in water-dispersible polymers for inks because of problems associated with solvent emissions from solvent-based inks.
Certain polyesters are water-dispersible as a result of sulfonate groups on the polyester backbone. These polyesters have been described in, for example, U.S. Pat. Nos. 3,734,874, 3,546,008, and 3,779,993.
Water-dispersible polyesters have been used in textile sizes and have been used to develop aqueous inks. Inks containing a water-dissipatable polyester are well known in the art as disclosed in U.S. Pat. Nos. 4,704,309 and 4,738,785. These inks have many desirable features, including excellent gloss and color development, good rewet characteristics, and low odor. However, because of the wide range of printing conditions and substrates used in the printing industry, a given ink formulation can have ideal properties for some applications and poor properties for other applications. U.S. Pat. No. 4,946,932 teaches preparation of polymer blends by polymerizing certain .alpha., .beta.unsaturated monomers in the presence of a polyester or polyesteramide material. These blends are generally useful in aqueous dispersions such as aqueous inks. Freeze-thaw stability is important in this class of products because without it the product must be very carefully protected, at additional cost, from freezing during shipping and storage. U.S. Pat. No. 4,812,510 teaches that certain latexes containing 0.05-15 parts of a certain acrylamide sulfonate compound (i.e., sodium 2-acrylamido-2-methylpropane sulfonate or "AMPS") have good mechanical, aging and heat stability, and stability with pigments.
I have surprisingly discovered that use of an acrylamide sulfonate compound for preparing polymer blends significantly improves the freeze-thaw stability of aqueous dispersions made from such blends. Such dispersions are useful in many applications such as adhesives, inks and other coatings.